The present invention of the application relates to an exhaust gas purification device provided in a diesel engine or the like, and more particularly, to an exhaust gas purification device for eliminating particulate materials (soot, particulate) and the like included in exhaust gas.
There is a known technique that a diesel particulate filter (DPF, hereinafter) is provided in an exhaust path of a diesel engine (engine, hereinafter) as an exhaust gas purification device, and exhaust gas from the engine is purified by the DPF (see Patent Document 1 for example). There is another known technique that an inner case is provided in an outer case to form a double-layer structure in a DPF, and an oxidation catalyst or a soot filter is incorporated in the inner case (see Patent Document 2 for example). There is also another technique that a case in which an oxidation catalyst is accommodated and another case in which a soot filter is accommodated are connected to each other in a DPF through a bolt-fastened flange such that the cases can be separated from each other (see Patent Documents 3 and 4 for example).
According to the DPF described in Patent Document 4, to connect, to each other, an upstream side case of a single-layer structure in which an oxidation catalyst is incorporated and a downstream side case of a single-layer structure in which a soot filter is incorporated, the upstream side case and the downstream side case are formed into cylindrical shapes having the same diameters, one of the cases is provided with an diameter-enlarged portion, the other case is tightly fitted into the diameter-enlarged portion of the one case so that the oxidation catalyst and the soot filter are disposed closely. If this configuration is employed, since a region in the cases between the oxidation catalyst and the soot filter is narrowed (radiating area is narrowed), there is a merit that probability of temperature reduction of exhaust gas between the oxidation catalyst and the soot filter can be suppressed.